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As frequent rainfall continues to replenish our soil profile with moisture, we can expect a very green spring across Texas this year. As temperatures warm, warm season grasses and weeds will come to life, including beautiful wildflowers. Unfortunately, along with the good, there will also be pesky weeds, including plants like the grassbur. It seems that the year following a drought, weeds are much more pronounced in our pastures, as thin grass stands allow weed seeds to germinate.

Field sandbur (grassbur) is a summer annual or perennial grassy weed that can be found in home lawns, sports fields, parks, along roadsides, and in improved Bermudagrass pastures and hay fields. This weed is especially adapted to dry, sandy soils but can be found growing in other types of soils as well.

The big problem with this weed is the sharp, spiny burs that are part of the inflorescence. The bur spines are stiff and can injure the mouths of animals and the hands and feet of people working in infested crops. Field sandburs (grassburs) generally start germinating in spring and continue to germinate until late summer or early fall and will continue to grow until the first hard frost or freeze occurs.

Until recently, few herbicide tools were available to help manage the grassbur in our Bermudagrass pastures. Now however, Prowl H2O, from BASF, has received a Supplemental label that will allow application to dormant Bermudagrass pastures and hay meadows for control of sandbur and other weed species (numerous annual grasses and small seeded broadleaf weeds), all of which are listed on the full label. This label will be in effect until December 2011.

The labeled rate for Prowl H20 on dormant Bermudagrass pastures and hay meadows is 1.1 to 4.2 quarts per acre. The higher rate is suggested for more dense infestations of targeted grasses and weeds or where a longer duration of residual weed control is desired. The timing for application is any time during winter dormancy and prior to weed germination. Ideally, activation of this herbicide is accomplished with 1 inch of precipitation following application.

Some additional restrictions apply, including: do not harvest Bermudagrass hay until 60 days after treatment, and do not harvest for forage or allow livestock to graze until 45 days after treatment. Prowl H20 can be used on all Bermudagrass varieties, but the stand must be established and have gone through at least one cutting before treatment. The use of Prowl H20 on rangeland is prohibited.

If you miss the opportunity to treat for grassburs when the Bermudagrass is dormant, another option might be available. Last year, EPA granted a crisis exemption for the use of Pastora herbicide, from DuPont, for control of emerged sandburs in Bermudagrass. Applications had to be made when the sandbur was less than 1.5 inches tall and/or across, and actively growing.

Moreover, applications of Pastora had to be made to Bermudagrass that was less than 4 inches tall following initial green-up in the spring or after cutting for hay. Tall, dense stands of Bermudagrass can intercept spray and reduce sandbur control. This application has not been approved for 2010; however, a request has been submitted to the EPA for another crisis exemption for this year, and DuPont hopes to receive a full federal label in the near future. At the date of this article, it is not legal to apply Pastora.

Pastora should not be applied to newly sprigged or newly planted Bermudagrass. Apply only to established Bermuda grass that is at least one year old. A follow-up application of Pastora may be necessary to control subsequent germination (flushes) of sandbur following the first application. To control sandbur species, apply Pastora herbicide at a broadcast rate of 1.0 to 1.5 ounces per acre.

No grazing or haying restrictions exist for this herbicide, and as always, read and follow all the label restrictions when utilizing this product. Again, this label has not been approved for 2010.

The control of grassbur in improved Bermuda grass pastures and hay meadows with herbicides should be part of an overall management plan that includes fertility management based on soil testing, adequate soil moisture, insect and rodent control along with best management agronomic practices.

Any references made to commercial products or trade names were made solely for educational purposes with the understanding that no endorsement or discrimination is implied by Texas AgriLife Extension Service or its agents.